Method of inhibiting foam formation in steam generating systems



METHOD OF INHIBITING FOAM FORMATION IN STEAM GENERATING SYSTEMS No Drawing. Application October 24, 1951, Serial No. 252,979

8 Claims. (Cl. 252-321) The present invention is concerned with a method for conditioning water for the prevention of excessive foaming, and for the diminution of existing foaming in steam boilers.

The present invention relates to a method for conditioning water particularly in steam generating systems operated at superatmospheric pressures for the prevention or reduction of foaming in such systems, for the prevention or reduction of moisture entrainment in the steam generated in these boilers and for generally improving the character of Water used in steam boilers and other steam generating systems.

Foaming of boiler water is not, as commonly thought, equivalent to an accumulation of foam on top of the surface of boiling Water as may occur, for instance, when soap solutions are agitated. The foam or froth obtainable by blowing air through or by stirring the soap solution accumulates on top of the water surface and presents a distinct water-froth interface. Such froth is the result of an equilibrium arrived at after a considerable time as a result of the interplay of various factors, such as surface tension, forces tending to establish a more or less organized surface layer, preferential adsorption and the like, and this interaction leads to The formation of relatively stable froth.

The development of foam in a liquid system being heated, however, may be due to the development of numerous gas or vapor nuclei on the hydrophobic surfaces of particles of matter suspended in liquid and/or absorbed on the heating surface. Normally, such numerous small bubbles will resist coalescence while rising through the liquid and will remain stable after reaching the liquid surface where they form a layer of froth or foam. The compositions used in the method of the present invention effectively bring about a pronounced decrease in the number of gas and vapor nuclei, and at the same time, the molecules of the compounds of the present invention rapidly spread out in the vapor-liquid interface and bubble film to disrupt the stabilizing forces, thus causing the immediate collapse of such vapor bubbles and destroying the froth or foam formation. The foaming of boiler water is due to the formation of a larger number of steam bubble nuclei on the heating surface which generates numerous small steam bubbles having the property of resisting coalescence while rising through the boiling water. The formation of such a large number of relatively small bubbles tends to expand the volume of Water without necessarily effecting the formation of a layer of stable froth on the top of the boiling water. Further, a water that forms a froth on agitation or blowing of air therethrough does not neces-' sarily always foam or expand on boiling. A differentiation may be made between the 'terms .foam inhibition and defoaming. Foam inhibition includes instances where a compound or substance when added to a liquid inhibits the initiation of foam formation, while defoaming" applies where a compound when added to a solution already in a foaming condition ef- States Patent 2,727,867 Patented Dec. 20, 1955 ICC both as defoamers and foam inhibitors, under certain' conditions.

One'of the major problems arising from foaming in boiler waters is the production of myriads of bubbles which fill the steam space and become entrained with the high velocity steam being withdrawn from the boiler. This light water carry over presents difiiculties in that it causes incrustation in the subsequent components of the boiler system.

Operation of evaporators for the production of feed water for boilers, and particularly on sea-going vessels, is constantly confronted with carry over problems resulting in the contamination of the boiler feed water with disastrous results. The concentration of ocean water salines in the evaporator also causes precipitation of calcium and magnesium salts therein which tend to stabilize Numerous types of organic compounds have previously been suggested for inclusion in aqueous systems having a tendency to foam for the purpose of minimizing such foam formation. One of the earliest compounds to be employed in this connection was castor oil. However, the use of castor oil Was found to beobjectionable because the anti-foaming effect achieved was transient. Experimental work has indicated that the probable life of castor oil in a boiler operating at a pressure of 200 pounds persquare inch gauge is on the order of 3 or 4 minutes or less. Further, it has been demonstrated that once castor oil is fed into a boiler, the tendency toward foaming is aggravated shortly after the feeding of castor oil to the boiler has been stopped. Hence, the use of castor. oil as an anti-foam agent requires that a constant rate of feed be maintained if satisfactory boiler operation is to be achieved.

Other organic compounds far more effective than castor oil from the standpoint of foam inhibiting effectiveness and effective boiler life have also been suggested and used. For the most part, however, these materials are insoluble in Water in the concentrations needed for satisfactory boiler operation, and. may range from oily liquids to waxy solids. In order to feed such material satisfactorily to the boiler feed water it isnecessary that such materials be first dispersed or emulsified. The process of emulsifying or dispersing such anti-foam agents is often difiicult and leadsto expensive operations both from the standpoint of the materials required to produce the emulsion and from the cost resulting from the necessary processing.

Another significant advance in the art of conditioning water for use in steam boilers to prevent foam formation is the joint use of a surface active agent with an anti-foam agent. Combinations of this nature have been successfully used to reduce or eliminate the so-called aerosol spray carry over resulting from entrainment of small globules of boiler water with the steam. The formation of suchglobules takes place when steam bubbles collapse or break down at the water-steam interface within the boiler. v

The present invention is based upon a discovery that certain non-ionic detergent compositions effectively inhibit the formation of foam, and collapse existing foam in steam generating systems operating at superatmospheric pressures. These compounds are quite unique as compared to the ordinary anti-foam compounds in that they are readily soluble in cold water and thereby eliminate the necessity ofemulsification and dispersion in the boiler feed water. Furthermore, as is true of any non-ionic detergent, the compounds used in the method of the present invention contain both a hydrophobic and a hydrophilic portion.

The compositions employed in the present invention are non-ionic detergent compounds having a hydrophobic portion consisting of a polypropylene glycol residue and a hydrophilic portion consisting of ethylene oxide linkages in proper balance. Surprisingly, this type of non-ionic detergent has excellent foaming properties when employed in aqueous systems at atmospheric pressures, but at pressures in excess of about pounds per square inch gauge, the compounds commence to exhibit significant foam inhibiting properties. At pressures in excess of pounds per square inch gauge, the foam inhibiting ability of these compounds is quite marked. This unique property of compounds employed in the present invention is particularly remarkable since it would be natural to assume that a compound which has no foam inhibiting effectiveness, and in fact increases foaming under conditions of atmospheric pressure, would not exhibit foam inhibiting properties at superatrnospheric pressures. Yet the compounds used in the present invention commence their foam inhibiting properties at pressures of about 10 lbs. per sq. in. gauge, and maintain these properties as the boiler pressure is raised.

An object of the present invention is to provide a method for conditioning water in steam generating systems for the prevention of foam generation and for the collapse of existing foam.

'Another object of the present invention is to provide a method for treating boiler waters to be used in steam generating systems such as boilers including the step of dispersing into the steam generating system an effective amount of a non-ionic detergent having both foam inhibiting and surface active properties in the same molecule.

Still another object of the present invention is to provide a method for minimizing the formation of foam and froth in steam generating systems through the use of a water soluble foam inhibiting agent.

' Still another object of the present invention is to provide a process for the minimizing of foam formation in steam boilers operated at superatmospheric pressures.

The compounds used in the method of the present invention have the following general formula:

G H: H3

The foam inhibiting non-ionic detergents are prepared from the polypropylene glycol by condensing the glycol with ethylene oxide, in the presence of a strongly alkaline catalyst such as solid sodium hydroxide, at slightly elevated pressures, the addition of the ethylene oxide occurring through oxy linkages to the same extent on each of the two hydroxyl groups of the polypropylene glycol. The amount of ethylene oxide added depends upon the final molecular weight desired in the product. If sufiicient ethylene oxide is added to bring the total molecular weight to approximately 7000 or above, the product is no longer liquid but a water soluble solid.

Compounds of the above mentioned type have been previously prepared and sold as detergent compositions under the trade name Pluronic. The physical characteristics of four members of this family of compounds are itemized below:

All of the above compounds are soluble in cold water and exhibit foam inhibiting properties at pressures of 10 lbs. per sq. in. or greater and particularly at pressures of at least 20 lbs. per sq. in. gauge. As far as I have been able to determine, there is no upper limit on the boiler pressures at which the compounds will operate satisfactorily as foam inhibitors and I have used pressures of 200 lbs. per sq. in. gauge and greater.

The amount of the foam inhibiting compound to be introduced into the boiler water, either into the feed water entering the steam generating system, or into the water already present in the boiler will depend to a large extent upon the solids content of the water being treated. Actually, as little as .1 part per million of the compound or less etfectively inhibits foam formation in boiler waters having a total dissolved solids content of as much as 400 grains per gallon. Obviously, larger amounts of the foam inhibiting material can be used where required, to increase the permissible concentration of solids without foaming.

It is usually desirable to add other water treating agents beside the foam inhibiting compound when treating boiler waters. Thus, a complete foam inhibiting formula might where x, representing the repeating hydrophobic building units has a value of at least 15, and y, representing the hydrophilic building units has a value of at least 3. The values of x and y are preferably adjusted in the molecule such that the resulting compound has a molecular weight in the range from about 1500 to 12000, and preferably between 2000 and 12000.

The compounds of the type described can be prepared in several manners. One method consists in reacting monomeric propylene glycol with a suflicient amount of propylene oxide to form a polypropylene glycol having the desired molecular weight to be achieved in the hydrophobic portion of the molecule. Alternatively, one mole of water may be reacted with one mole of propylene oxide, resulting in the rupture of the propylene oxide ring to form propylene glycol. Sulficient quantities of propylene oxide are then added to the thus formed propylene glycol in the presence of solid sodium hydroxide as a catalyst until a hydrophobic unit of the proper weight has been built up. The resulting propylene glycol has the following formula:

Percent Soda ash 42 Maracell E extract 50 Sludge conditioner 6 Pluronic F-68 2 The sludge conditioner referred to above may be a material such as carboxymethyl cellulose, starches, so dium alginate, quebracho tannin, chestnut tannin, or a newly developed polyacrylate sludge conditioner more particularly described in copending application Serial No. 254,808, filed November 3, 1951, and assigned to the same assignee as the present invention. Maracell E is a modified lignin sulfonate derived from sulfite waste liquors.

Alternatively, the organic sludge conditioners may be eliminated with an increase in the soda ash content to yield an acceptable foam inhibiting composition. However, I prefer to use the organic additives of the type previously described in combination with the foam inv I hibiting agent as it appears that the anti-foaming activity prises adding to saidsystem an amount effective to inhibit of such anti-foam agents is usually enhanced by such foaming of a non-ionic detergent compound having the organic additives. formula:

A still further simplified foam inhibiting formula may where x is at least and y is at least 3, the molecular consist solely of the combination of soda ash in an weightof said compound being not in excess of 12000, amount of 98% by weight, in combination with one of and generating steam from said system at a pressure of the non-ionic detergents of the type described in an 10 at least 10 lbs. per sq. in. gauge. amount of 2% by weight. The above formulations are 3. The method of inhibiting foam formation in steam given for purposes of example only, and it will be appregenerating systems using water having a tendency to foam ciated that the percentages of the anti-foam agent may and operated at superatmospheric pressures which combe widely varied depending upon the nature of the water prises adding to said system an amount effective to inhibit treated. In most cases, one pound of the composition, 5 foaming of a non-ionic detergent compound having the including a few per cent of the non-ionic detergent will formula:

suflice to treat from 4,000 to 20,000 gallons of feed water. where x and y are integers, and of such value that the From the foregoing, it will be appreciated that the molecular weight of the resulting compound is in the range method of the present invention represents a distinct imfrom 1500 to 12000, and generating steam from said sysprovement in the art of treating aqueous systems to pretem at a pressure of at least 20 lbs. per sq. in. gauge. vent or minimize the formation of foaming upon boiling 4. The method of inhibiting foam formation in steam under superatmospheric pressure. The agents used in the 5 generating systems using water having a tendency to foam water treating process are soluble in cold water and thereand operated at superatmospheric pressures which comfore eliminate the need of emulsifying or dispersing agents prises adding to said system an amount effective to inhibit in the compounding of the water treating materials. foaming of a non-ionic detergent compound having the Furthermore, the water treating agents are stable even formula:

CH3 cm on, HO-CHzCHz-(O-CH:CH:),OHCHz-O(AHCHO)=-AHCHzO-(CHzCHr-O)rCHzCHaOE under high pressure and are sufiiciently surface active clue where x and y are integers, and of such value that the to the hydrophilic linkages in the molecule to minimize molecular Weight of the resulting compound is in the range aerosol formation in the steam space of the boiler. 35. from 2000 to 12000, and generating steam from said sys- Since the compounds used in this invention are essentem at a pressure of at least 20 lbs. per sq. in. gauge. tially water soluble and non-ionic, they may be success- 5. The method of inhibiting foam formation in a steam fully used in treating the water prior to lime-soda softengenerating system operating at superatmospheric pressures ing or coincidental therewith without danger of the foam which comprises adding to said system, in an amount efinhibiting compounds being coagulated or adsorbed in fective to inhibit foaming, afoam inhibiting, non-ionic dethe coagulant to any appreciable extent. Also these foam tergent compound having the formula:

CH3 CH3 CH3 HOCH2CH2(OCH2OH2) O( JHCHQO(JHCH2-O)r-IHCH2O-(CH2CH2O)rCHzCHzOH inhibiting compounds may be added prior to passing the where x has a value of from 22 to 30, and y has a value water to be used for boiler feed purposes through a of from 58 to 63, and generating steam from said system zeolite softener or an ion exchange resin if such method at a pressure of at least 10 lbs. per sq. in. gauge. of addition would be advantageous in any special appli- 6. The method of inhibiting foam formation in a steam cation. generating system operating at superatmospheric pressures It will be understood that modifications and variations which comprises adding to said system, in an amount efmay be effected without departing from the scope of the fective to inhibit foaming, a foam inhibiting, non-ionic denovel concepts of the present invention. tergent compound having the formula:

OH; CH: CH; HO-CH:OHa-(0CHzOHz),,OC 3HCH2O(lHCHzO)=( JHCH2O(CHzCH2O),,CH2CH:OH I claim as my invention: where x has a value of from 22 to 30, and 3 has a value 1. The method of inhibiting foam formation in steam of from 10 to 12, and generating steam from said system generating systems using water having a tendency to foam at a pressure of at least 10 lbs. per sq. in. gauge. and operated at superatmospheric pressures which com- 7. The method of inhibiting foam formation in a steam prises adding to said system an amount effective to inhibit 60 generating system operating at superatmospheric pressures foaming of a non-ionic detergent compound having the which comprises adding to said system, in an amount efformula: fective to inhibit foaming, a foam inhibiting, non-ionic de- CH; CH3 CH HO-CHzCHz-(O-CHzCHt)|-O-HCHzO-(27HCHzO)ir-JZHCHgO-(CHzCHz-O) -CHzCHzOH where x and y are integers, and of such value that the tergent compound having the formula:

CH; om CH: HO-CHzOHa-(O-OHaCHa) -O-(lIHCHr-O-(JJHCHr-O)r-(EHCHzO-(CHzCHz-O),-CHzCHzOH molecular weight of the resulting compound is in the range where x has a value of from 22 to 30, and y has a value from 2000 12000 and generating Steam d of from 3 to 4, and generating steam from said system at tern at a pressure of at least 10 lbs. per sq. in. gauge.

2. The method of inhibiting foam formation in steam a pressure of at least Per g generating systems using water having a tendency to foam The method of mhlbltmg foam formauon a steam and operated at superatmospheric pressures which comgenerating system operating at superatmospheric pressures which comprises adding to said system, in an amount efwhere x has a value of about 18, and y has a value of from fective to inhibit foaming, a foam inhibiting, non-ionic detergent compound having the formula:

CH3 CH: CH: HO-CHzCHr-(O-CH2OH2),O(5HCH2O-((BHOHg-O)r-HCHzO-(CHzClfi-O) -GHgCHzOH References Cited in the file of this patent UNITED STATES PATENTS sure of at least 10 lbs. per sq. in. gauge.

2,575,276 Jacoby et a1 Nov. 13, 1951 2,575,298 Ryznar Nov. 13, 1951 2,674,619 Lundsted Apr. 6, 1954 13 to 18, and generating steam from said system at a pres- 

1. THE METHOD OF INHIBITING FOAM FORMATION IN STEAM GENERALLY SYSTEMS USING WATER HAVING A TENDENCY TO FOAM AND OPERTED AT SUPERATMOSPHERIC PRESSURE WHICH COMPRISES ADDING TO SAID SYSTEM AN AMOUNT EFFECTIVE TO INHIBIT FOAMING OF A NON-IONIC DETERGENT COMPOUND HAVING THE FORMULA 